1. The Field of the Invention
The field of this invention lies within the blood filter art as it pertains to blood filtration during surgery. It more specifically relates to those blood filters that remove foreign matter and bubbles from blood passing in an extracorporeal blood circuit. The extracorporeal blood circuit often includes an artificial heart-lung machine or oxygenator. It can also include an artificial kidney as well as devices for separating blood cells and plasma components.
2. Prior Art and Improvements Over the Art
Many blood filters are known in the art. One particular related blood filter is that described in U.S. Pat. No. 4,919,802 which issued Apr. 24, 1990, entitled BLOOD FILTER, naming Yoshiro Katsura the inventor.
A second related patent is U.S. Pat. No. RE 32,711, reissued Jul. 12, 1988 and its original patent U.S. Pat. No. 4,411,783 respectively entitled ARTERIAL BLOOD FILTER WITH IMPROVED GAS VENTING naming Duane D. Dickens, and Francis M. Servas as inventors.
The U.S. Pat. No. 4,919,802 (802 Patent) specifically is directed toward a blood filter having a gas or air bubble separating section. The bubble separating section includes a conical top overlying a cylindrical chamber. The conical top allows gas or air bubbles to separate from the blood for discharge through a centrally placed air discharging vent. It relies upon a swirling flow or vortex within the filter chamber or container and conical top to create a de-bubbling effect.
The 802 Patent is specifically directed toward an inlet conduit that extends horizontally for introducing blood into the filter chamber. Further to the extent of delivery, the axis of the inlet conduit extends substantially parallel to a tangent line of the generally cylindrical filter chamber at the connection between the chamber and the inlet conduit, but is spaced a certain distance from the tangent line in a plane perpendicular to the axis of the cylindrical chamber.
In effectuating delivery of the blood into the chamber, the inlet conduit extends on a horizontal plane in a horizontal curved path of consistently decreasing radius, R1, toward the radius, R2, of the inner chamber from approximately its inlet to anywhere from 135.degree. to 225.degree. along the circumference of the chamber from its initial introduction point.
The U.S. Reissue Pat. No. 32,711 (711 Patent) also relies upon a substantially horizontal delivery conduit in a tangential direction which is not displaced as in the 802 patent. The horizontal input stream of blood is directed away from the central air vent. The patent teaches that this condition avoids interference with the venting. Further to this extent, it is seen that the horizontal delivery conduit delivers blood in the same manner as the 802 Patent around the interior wall portion of the blood filter chamber to create a vortex.
The 711 Patent further relies upon a sloped inner portion or filter cap element. The upper surface of the filter cap is symmetrical as to the longitudinal axis of the entire housing or chamber. The filter cap, furthermore, has its highest point at the center. A critical feature of the filter cap element is to exclude any localized points or regions of minimum height such as dimples, grooves, valleys and the like. Overlying the center on top of the filter cap is a dome shaped cover or lid which has a vent centrally oriented with respect to the axis of the entire filter chamber or body and the axis of the filter.
The teaching of both the 802 and the 711 Patents are directed toward a horizontal inflow which supposedly maintains laminar flow. This supposedly avoids the problem associated with the flow of the inlet blood impinging against the blood that is already in a swirling condition causing a disturbance in the blood inflow. In effect, the thought is to prevent turbulence so that blood and entrained air bubbles can readily separate.
In effect, the foregoing teachings of the substantially horizontally delivered blood flow, the tangential delivery as in the 711 patent and the tangential delivery as in the 802 patent which is parallel to and displaced from a tangent line of the chamber lying in a horizontal plane perpendicular to the axis of the chamber, as well as the symmetrical central filter cap of the 711 patent and the 802 patent, and the overall concept of bilateral symmetry with respect to the centrally placed air vent in the cap or the lid of the filter chamber have fundamentally taught away from the invention as established herein.
In particular, the aspects of the horizontal delivery of blood have been particularly noted. The Applicants herein have found that in preference to the horizontal delivery of blood, that an upward angular delivery of blood in the direction of the lid or top cover of the blood filter chamber is not only efficacious but improves performance substantially.
The upward momentum of the blood causes it to swirl around the top of the cover one or more times before it starts to flow downwardly. This swirling blood flow movement allows for entrained air bubbles to be removed in a more natural manner. The entrained air bubbles are placed in a natural state of buoyancy upwardly toward the offset vent of the filter of this invention. In allowing the directional component of the blood to achieve an upward vectorial velocity, the entrained air is also removed through its natural buoyancy being enhanced as to its direction of movement.
The upwardly directed blood inlet of this invention is deemed to be a significant step over the prior art in allowing the disassociation of air from blood to be filtered.
A second feature of the invention with respect to the prior art is an offset air vent. The offset air vent allows the placement thereof to be in the direction overlying the vortex. The upward velocity component of the delivered blood forms a vortex which is shifted or offset from the axial center of the blood filter chamber and lid. By placing the air vent overlying the general area of the shifted vortex, the entire function of disassociation and removal of entrained air through the offset vent is enhanced. This results in a non-conical filter chamber cover or lid.
Another feature of this invention is the conduit axis of delivery is angularly offset upwardly from a tangent line to the radius of the cylindrical filter chamber. By angularly offsetting the delivery of the blood upwardly into the filter chamber at the initial stages along and within a gently rising spiral channel, it is believed that less hemolysis is encountered due to the gentle nature of the introduction of the blood.
Another feature of this invention is that the axis of the introductory conduit at the point of introduction between the filter chamber and the inlet conduit is perpendicular to a line lying in a plane which is not perpendicular to the central axis of the filter chamber. It is believed that this feature enhances the release of entrained air from the blood when combined with the other features of the invention.
Another feature of this invention is the aspect of the air vent in the filter chamber cover being offset from the the axial center of the filter cap and filter, and filter chamber. This enhances the overall placement of the vortex while at the same time creating a non-tangential delivery of the blood in its flowing relationship.
A further feature of this invention relies upon the nature of the filter cap having the bottom edge chamfered and located below the inlet conduit to prevent entrained air bubbles from being retained under the filter cap.
A further feature of this invention that cuts down on hemolysis is the smooth and rounded delivery conduit. This allows the flow of blood to flow in a rounded smooth channel conforming to the configuration of the inlet conduit. This smooths the nature of the delivery of the blood so that it is not abruptly changed in direction, or introductory conduit configuration. The net result is lower turns and dramatic changes in blood flow which it is believed helps to lower the overall hemolysis of the blood to prevent undo damage to the cells thereof.
Another feature of the invention over the prior art is that the invention allows for a bypass of the filter through an integral bypass channel. This allows for the flow of blood to take place through the entire extracorporeal circuit by merely shifting introduction from the inlet of the arterial filter to the bypass circuit. This creates a continuity of flow with fewer components and a simpler circuit design over a standard bypass circuit.
In essence, this invention is believed to be a step over the prior art by providing upwardly angular introduction of blood into a filter for improved disassociation of entrained air. It further enhances the function by shifting the vortex in the direction of an offset air vent while at the same time allowing for improved flow features and non-entrapment of air in certain portions. The aspects of providing for an integral bypass also enables this invention to be a step over the art in allowing for ease and facility of use during its inclusion in the extracorporeal blood circuit of a user. And, due to its compact size, reduces the volume of fluid required in the extracorporeal circuit.